Light output power versus current, emission spectroscopy and far-field emission patterns have been used to characterize microcavitylight emitting diodes (MC-LEDs). Evidence that microcavity effects lead to enhanced emission properties is provided by changes in the total emitted light output power, as well as the electroluminescencespectra of the MC-LEDs. Compared to a conventional noncavity type LED structure, enhanced efficiency and narrow spectral linewidths have been observed for the MC-LEDs over a wide range of cavity detunings and cavity Q values. Evidence that control of the cavity detuning leads to temperature insensitive output characteristics is provided by changes in the temperature dependence of the slope efficiencies extracted from the light output versus current characteristics. Variations in the emitted radiation patterns as a function of current injection are also reported demonstrating the important role of the cavity detuning on the emission properties of MC-LEDs.

An analysis is made of spot patterns generated in a liquid crystalspatial light modulator with optical feedback from the point of view of controlling generation of spots. The conditions for forming solitary spots were analyzed using a theoretical model which fits the experimental device well. Phenomena observed in experiments such as spontaneous birth, motion, and merging of spots is reproduced in numerical simulation with the model. It is shown how parameters characterizing nonlinearity, diffraction, and diffusion can be designed for stable spots and stable spot motion.

We have fabricated a vertically aligned 4-domain nematic liquid crystal display cell with thin film transistor. Unlike the conventional method constructing 4-domain, i.e., protrusion and surrounding electrode which needs additional processes, in this study the pixel design forming 4-domain with interdigital electrodes is suggested. In the device, one pixel is divided into two parts. One part has a horizontal electric field in the vertical direction and the other part has a horizontal one in the horizontal direction. Such fields in the horizontal and vertical direction drive the liquid crystal director to tilt down in four directions. In this article, the electro-opticcharacteristics of cells with 2 and 4 domain have been studied. The device with 4 domain shows faster response time than normal twisted-nematic and in-plane switching cells, wide viewing angle with optical compensation film, and more stable color characteristics than 2-domain vertical alignment cell with similar structure.

In this work we report a room temperature green upconversion in Er-doped fluoroindogallate glasses, pumped at 833 nm. The rise time and stationary intensity of the transition as a function of laser intensity were monitored. Some possible pumping mechanisms are discussed in detail, and it is concluded that the main pumping route may be described in terms of the looping mechanism. It is also shown that cross relaxation among neighboring pairs of ions is near the threshold value to achieve the photonavalanche region.

A finite-difference time-domain scheme in a nonorthogonal coordinate system is presented to calculate the band structure of a two-dimensional photonic crystal consisting of a skew lattice. The method can be used for a photonic crystal of complicated configuration, such as a photonic crystal with both dielectric and metallic inclusions. The method is verified by comparing with the results obtained by other methods for some special cases. The band structure of a photonic crystal with a dielectric layer coated on a metallic cylinder as an inclusion is studied. For such a case, it is noticed that both the dielectric and metallic characteristics of the band structure are inherited.

A mathematical model describing the coupling of electrical, optical and thermal effects in semiconductor lasers is introduced. Through a systematic asymptotic expansion, the governing system of differential equations is reduced to a single second-order boundary value problem. This highly nonlinear equation describes the time-independent maximum temperature in the boundary layer adjacent to the mirror facet. The solution of the problem is a multi-valued function of current. The graph of the maximum steady-state temperature as a function of current gives a fold-shaped response curve, which indicates that no bounded steady state exists beyond a critical value of current. For certain device parameters and initial conditions, thermal runaway occurs. A mechanism for the sudden mode of semiconductor laser failure is described in terms of thermal runaway.

Schottkyphotodetectors were developed for solar ultraviolet A and B detection. Modeling is performed by developing programs of simulation leading to the most suitable device structure such as doping density, semiconductor thickness, etc. Simulations allow us to determine the most appropriate parameters

A large laser induced increase of light absorption has been observed in free-standing porous silicon films, in the wavelength range 500–700 nm. Thermal origin of the observed modulation is suggested by two hitherto unreported observations: the spectral dependence and the comparison between the time decay of modulation with photoluminescence. A simple thermal model, taking into account the porosity of the porous silicon film, provides a good fit over the probed spectrum.

The use of a simple capacitive discharge as a driver for an x-pinch soft x-raysource is demonstrated. The 30 kV, 4 kJ capacitive discharge had a quarter period of 1.2 μs, peak current of 320 kA, and current rise of X-pinch x-ray emission was characterized by pinhole photography and solid-state detectors.Soft x-ray emission (800 eV–4 keV) was observed in both single and multiple bursts, with yields from 180 mJ for aluminum to 1.5 J for tungsten wire x pinches. X-ray emission from x pinches was higher than z-pinch emission from the same materials using the same power source.Hard x-ray emission (>8 eV) from the x pinch was lower with the long pulse capacitive discharge than with a 360 kV pulsed power driver delivering 100 kA peak with a rate of current rise of Visible photography and laser-based schlieren photography showed that the x pinch was asymmetric about the crossing point of the wires. This asymmetry is due to the influence of electron beamgeneration at this point.

Laser induced fluorescence has been used to measure the spatial distribution of the two lowest energy argon excited states, and in inductively driven plasmas containing argon, chlorine and boron trichloride. The behavior of the two energy levels with plasma conditions was significantly different, probably because the level is metastable and the level is radiatively coupled to the ground state but is radiation trapped. The argon data are compared with a global model to identify the relative importance of processes such as electron collisional mixing and radiation trapping. The trends in the data suggest that both processes play a major role in determining the excited state density. At lower rf power and pressure,excited state spatial distributions in pure argon were peaked in the center of the discharge, with an approximately Gaussian profile. However, for the highest rf powers and pressures investigated, the spatial distributions tended to flatten in the center of the discharge while the density at the edge of the discharge was unaffected. The spatially resolved excited state density measurements were combined with previous line integrated measurements in the same discharge geometry to derive spatially resolved, absolute densities of the and argon excited states and gas temperature spatial distributions. Fluorescence lifetime was a strong function of the rf power, pressure, argon fraction and spatial location. Increasing the power or pressure resulted in a factor of 2 decrease in the fluorescence lifetime while adding or increased the fluorescence lifetime. Excited state quenching rates are derived from the data. When or was added to the plasma, the maximum argon metastable density depended on the gas and ratio. When chlorine was added to the argon plasma, the spatial density profiles were independent of chlorine fraction. While it is energetically possible for argon excited states to dissociate some of the molecular species present in this discharge, it does not appear to be a significant source of dissociation. The major source of interaction between the argon and the molecular species and appears to be through modification of the electron density.

A numerical solution for the metallic-plasma-neutral-gas structure generated in a low-pressure arc is presented. The equations correspond to a spherically symmetric fluid-like steady model, valid for the outer region of the arc, and describe the ion slowing down by elasticscattering with the neutral particles. Technically, the obtention of the profiles of different magnitudes is complicated due to the existence of a critical point in the steady-state system of equations. The proposed approach to overcome this difficulty is to solve instead a pseudotransient system of equations which rapidly and efficiently relax to the stationary state. By employing this numerical method of second-order accuracy in space, the plasma and neutral gas density, the electron and ion drift velocities, the electron and neutral temperatures, and the electrostatic potential profiles are obtained from the border of the arc channel up to the discharge chamber wall. It is found that the value of the neutral gas filling pressure strongly influences the plasma density and plasma potential distributions. An important result is that metallic ions emitted from the arc channel deliver their kinetic energy to the filling gas in a gradual manner, up to a pressure-dependent point beyond which they move to the walls sustained against collisions with the gas by a self-consistent electric field. Near the mentioned point, the metallic ion density presents a peculiar behavior, showing an increase that is more pronounced at high pressures; a pattern also evident in the electrostatic potential.

A spatially averaged (well mixed) reactor model was used to simulate a power-modulated (pulsed) high density oxygen discharge. Chemistry involving the high energy oxygen metastable molecules was included in the simulation. This chemistry was necessary to capture the experimentally observed increase in the negative ion density in the afterglow of the pulsed discharge. As the electron temperature drops in the afterglow, the rate coefficient of electron attachment with increases several fold. The wall recombination probability of oxygen atoms affected the density drastically. For the conditions studied, the maximum density in the afterglow increased with pressure, decreased with power, and showed a maximum with pulse period. The time in the afterglow at which the peak density occurred decreased with pressure and power, and was independent of the pulse period. Knowing the temporal evolution of in the afterglow may be important for applications requiring extraction of negative ions out of the discharge.

A model is developed for self-consistently calculating the gas temperature in a direct current argon glow discharge, used for analytical spectroscopy. The power input into the argon gas due to elastic (i.e., kinetic energy transfer)collisions of ions, and fast Ar atoms, sputteredCu atoms and electrons with the argon gas atoms is calculated with Monte Carlo models. This power input is used in a heat transfer model to calculate the gas temperature. The amount of power input, the contributions of the various input sources, and the resulting gas temperature are calculated for a wide range of voltages, pressures, and currents, typically applied in analytical spectroscopy. It is found that the temperature can increase significantly at high voltages, pressures, and currents (up to a factor of 3 compared to absolute room temperature).

Ion charge state distributions of vacuum arc ion sources are correlated to the arc operating voltage. Recent research has shown that an enhancement of ion charges via an increase of the arc voltage can be achieved utilizing the transient processes that accompany an arc current spike. The idea investigated is to further enhance the ion charge states by multiple current pulses. It is shown that although the ion charge states are enhanced compared to quasi-dc operation, the application of a sequence of pulses does not lead to the desired additional increase in charge states. This can be attributed to the additional plasma production that is caused by higher arc currents: The additional power supplied to the plasma is distributed over a larger number of plasma particles. One can expect that in the limiting case of many current spikes, the ion charges state distribution approaches the one known for arc plasmas at higher discharge current.

We have investigated the possible role of redeposition of silicon–chloride etching products on profile evolution by studying the influence of etching product partial pressure on the surface layer formed during chlorine plasma etching of -masked -type Si(100). Samples were etched with high and low etching product -to-etchant concentration ratios by changing the flow rate (1.4 or 10.0 sccm, respectively) at a constant pressure of 4 mTorr. Compositional analysis was performed using angle-resolved x-ray photoelectron spectroscopy(XPS). Electron shadowing and differential charging of the insulating regions were exploited to spatially resolve the composition of the trench sidewalls and bottoms (2.0, 1.0, 0.5, 0.3, and wide). Chlorine content and stoichiometry of the etchedsurfaces were determined by quantifying the XPS intensities of both the peak and the silicon chloride containing tail of the peak. Comparisons of chlorine content and stoichiometry were also made to unmasked Si areas etched on the same samples. For trenches etched with 10 sccm the chlorine coverage equivalent to ∼3 monolayers) and the silicon chloride stoichiometry were identical for the unmasked Si areas and the bottoms of the trenches. The trench sidewalls, however, contained roughly 50% less Cl than the unmasked areas, all in the form of SiCl. Virtually identical results were obtained for trenches etched with 1.4 sccm indicating that increased etching product concentrations do not result in the formation of a thick, passivating sidewall layer on trench sidewalls during plasma etching of Si masked with

Optical absorptionspectra and the annealing behavior of hydrogen (H)-point defect complexes in carbon (C)-doped Si after hydrogenation were investigated. Specimens of C-doped Si (C concentration: were sealed in quartz capsules together with gas and were annealed at a high temperature for 1 h followed by quenching in water. We measured the optical absorptionspectra at about 7 K with a Fourier-transform infrared spectrometer. The (V: monovacancy) defect was almost annealed out at 600 °C. The formation energy of the defect in C-doped Si was estimated to be about 3.2 eV from the quenching temperature dependence of the 2223 cm−1 peak. The observed 2192 and 2203 cm−1 peaks are probably due to the defect, which captures one H atom during annealing and become the defect. After annealing at 700 °C, we observed two absorption peaks at 2093 and 2086 cm−1, which are probably due to Si–H stretching vibration of H on internal surfaces of voids. From these assignments, it was found that V is introduced into C-doped Si at high temperatures, although it is known that C introduces I into Si at high temperatures.

We use positron annihilation to study vacancy defects in GaAs grown at low temperatures (LT–GaAs). The vacancies in as-grown LT–GaAs can be identified to be Ga monovacancies, according to their positron lifetime and annihilation momentum distribution. The charge state of the vacancies is neutral. This is ascribed to the presence of positively charged antisite defects in vicinity to the vacancies. Theoretical calculations of the annihilation parameters show that this assignment is consistent with the data. The density of is related to the growth stoichiometry in LT–GaAs, i.e., it increases with the As/Ga beam equivalent pressure (BEP) and saturates at for a BEP⩾20 and a low growth temperature of Annealing at removes Instead, larger vacancy agglomerates with a size of approximately four vacancies are found. It will be shown that these vacancy clusters are associated with the As precipitates formed during annealing.

In this work, we investigate (i) the interaction of silicon interstitial atoms during thermal oxidation of silicon with a dislocation loop layer positioned at different distances from the surface as well as (ii) the interaction between two loop layers positioned at different depth distances. In both experiments, interstitials are injected by surface oxidation. The results show a linear dependence of the injection flux of interstitials with the inverse of the distance of the loop layer from the surface and a small leakage (16%) of the injected interstitials escaping from the upper and becoming bounded to the deeper loop layer. The experiments are performed using the wafer bonding technique that allows versatility on their design.

Damage in Si induced by irradiation with various light/medium mass ions at elevated temperatures and high doses was studied using Rutherford backscatteringspectroscopy, cross-section transmission electron microscopy, and high resolution x-ray diffraction. The results obtained have shown that there is a marked variation in the damage accumulation for different ion species. For and ions a distinct layer with a low level of damage presenting negative strain is formed at the surface. It has been found that the magnitude of the strain does not correlate with the energy deposited in the collision cascades. In the cases of and implantation, a low damage accumulation occurs near the surface but no negative strain is formed. In contrast to the and cases, with the increase of the or dose the damage profile stretches almost to the crystal surface. It is proposed that in addition to the mechanism of spatial separation of Frenkel pairs taking place in the collision cascades, the ability of the implanted ions to form precipitates and complexes with Si atoms noticeably influences the damage formation during implantation at elevated temperatures.

Observations on deep levels introduced in silicon by 1 MeV electron irradiation are reported using boron- or gallium-doped Czochralski (CZ) grown Si space solar cells with different doping concentrations, deep level transient spectroscopy analysis has been carried out to detect the radiation-induced deep levels. Present results provide evidence for new defect states in addition to those previously reported in gallium- and boron-doped Si. The combined boron and gallium data provide enough information to gain valuable insight into the role of the dopants on radiation induced defects in Si. The dominant donor-like electron level at in boron-doped Si has not been observed in gallium-doped CZ-grown Si. A noticeable suppressing generation of the radiation-induced defects in gallium-doped Si is also observed, especially hole level which is thought to acts as a recombination center.